DK2286897T4

DK2286897T4 - Device for reducing NOx and N2O content in gases

Info

Publication number: DK2286897T4
Application number: DK10014425.2T
Authority: DK
Inventors: Meinhard Dr Schwefer; Michael Groves; Rolf Dr Siefert; Rainer Maurer
Original assignee: Thyssenkrupp Ind Solutions Ag
Priority date: 2002-06-13
Filing date: 2003-06-10
Publication date: 2019-01-21
Also published as: EP2286897B1; PL374320A1; CA2489109A1; EP1515791B1; PL209337B1; PT2286897E; EP1515791A1; MX264791B; ZA200409479B; DK1515791T4; US20060051277A1; AU2003236729A1; ES2369078T5; CN100337725C; CA2489109C; WO2003105998A1; EP2286897A1; CN1658956A; EP1515791B2; RU2318581C2

Abstract

To reduce the content of NO 2 and NOx in process and exhaust gases, they are passed over two catalyst beds (4,5) in succession, containing one or more zeolites charged with iron, between the gas inflow (1) and outflow (2). An agent for the reduction of NOx is fed (3) into a mixer (6) between the catalyst beds, and the bed temperatures are set at = 500 [deg] C. The gas pressure is adjusted to at least 2 bar in both beds. The spatial speed is selected through the ring channel gaps (7-10) at the beds, so that the NO 2 content is degraded in the first bed at the most by 90 % of its content on the entry of the gas into the bed and is degraded in the second bed by at least 30 % of the content on entering the second bed.

Description

Device Lor reducing the NO,; and KhC> content of gages

The present, invention relates to an apparatus for carrying out methods for reducing the content of nitrogen oxides in gases, in particular in process gases and offgases.

In many processes, for example combustion processes or in the industrial manufacture of nitric acid,- an offgas is -produced that is- laden with nitric oxide ho, nitrogen dioxide (together designated as HCp) and nitrous oxide N2O. Whereas NG and KQ:.> have long been known to he compounds with relevance to environmental pollution (acid rain> smog formatIon) and limits for their maximum permissible emissions have been established globally., in recent years nitrous oxide has increasingly also been afc the center of attention for environmental protection, as this contributes to a not inconsiderable extent to degradation of stratospheric ozone and to the greenhouse effect. Therefore, for reasons of enviroHmental protection, there is a pressing need for technical solutions for removing the nitrous oxide emissions together' with, the K-Q* emissions.

For separata removal of £10 on the one hand and on the other hand, numerous possibilities are already known:.

In the case of reduction, selective catalytic reduction (SCR) of D0x by means of ammonia in the presence of vanadium-coxitaining TiOa catalysts may be mentioned In particular (see, for example, G, Ertl, H. Kn.6sin.gfer J. Weitkamp: Handbook of heterogeneous Catalysis, Vol. 4, pages 1633:-1668, VCH Welnhsim (1397)5., Depending on the catalyst, this can take place at temperatures from approx, 15Q°C to approx.. iSO^C and makes N0x degradation of more than 90% possible. it Is the most used variant for lowering hCg from offgases of industrial processes.

There are also methods teased, on teolite catalysts for reduction of K0,;, which take place using various reducing agents. As well as Cu~exchanged zeolites (ef„ e.g. EP-A-0 91i8 5S} , mainly iron-containing rooiites appear to be of interest, for practical, application.

Thus, US-A--4,571,329 claims a method for reducing N0x in. a gas. Which consists to at least 50% of NQ2i by means of ammonia in the presence of an Fe-zeolite. The ratio of ffig to NG2 is at least 1,3. According to the taethod described here, SOX-containing gases are reduced with ammonia, without leading to formation of 1T2O as bypr oduct,. US 5,4 51,3.87 describes a method for selective catalytic reduction of NOX with W3 over iron-exchanged zeolites, which is carried out at temperatures around 4006G.

In contrast to lowering the 110x content in offgases, which has been established in industry for many years, there are only a few technical processes for removing XljO. which mostly aim at thermal or catalytic degradation of the SLO, A review of catalysts that have been shown, in pririciple to be suitable for degradation and reduction of nitrous oxide is given by Kapteijn et al, (Kapteijn F, et al., Appl, Cat, St Environmental. 9 (1.335} 25--64) ,

Once again, Fe~ and Cu~zeoiite catalysts appear to be particularly suitable, and they either bring about pure decomposition of ΐ;20 to N2 and 02 (US-A--5,171,553), or they are used for the catalytic reduction of d2o by means of 17¾ or hydrocarbons to it and H20 or CO-,,

Thus, TP~A~07 06-0 125 describes a method for reducing K20 with KS3 in the presence of iron-containing zeolites of the pentasil type at temperatures of 4 50°C. The N;:0 degradation achievable with this method is 71%.

Mauve tin. et al. give,. in Cat a 1.. Lett. 6.2 (.1339) 41-44. a relevant review of the suitability of various iron-exchanged zeolites of the MOS, MFX, BSA, FBR, BU, M&2. and OFF type. .According to this, a vore than 90% d20 reduction by addition of. 141¾ below 50 9° C can Ohly be achieved in the case of Fe~BSA.

As well as the aforementioned methods for separate removal of h2O ancl N0x, there are also methods for combined removal, which can take place using a single cs.c s A method is known from WG-A-0G/4871S in which ail NQX-and N20-containing offgas is led at temperatures between 200 and. S00aC over an iron zeolite catalyst of the beta type ·{«. BSA type) , wherein the of fgas additionally contains 14¾ in a quantitative ratio between fi,7 and 1.4 relative to the total amount of M0x and W). NH3 serves here as a reducing agent both for ϊ?Οχ and for h20. The method admittedly operates at temperatures of less than SQCPG, but like the aforementioned method it has the fundamental drawback that for removal of the d20: content, a roughly equimolar amount of reducing agent (in this case ®h3) is required.. A method Is know, from WG-A-oi/51,181 for removing KQX and N20, in which, a process gas or offgas is led through, two reaction zones, which, contain zeolites loaded with iron as catalysts. In this, KUO is decomposed in the first, reaction zone, between the first and the second reaction zone ammonia is added to the gas mixture, and K'0x is reduced in the second reduction zone. it was found, surprisingly, that the effectiveness of the aforementioned method can he. Increased markedly if the .lowering of the Na0 content, to the desired degree of degradation, not only taken place in the first reaction zone, but the reaction zone for NOæ reduction can also foe utilised tor lowering N20, This became possible as it W found, surprisingly, that when using zeolite catalysts loaded with iron, a simultaneous SCy reduction (e.g. by means of NH3) and N20 decotsposition is possible. The contribution to N?0 decomposition in the second reaction step is .particularly large when, tbs method is carried out at increased pressures, i.e. at pressures above 2 bar, preferably above 4 bar.

The problem to be solved by the present invention is to provide a device with which simple, but economical processes can be carried out, which provide good conversion rate© both for iKy and for %.O degradation and are characterized by minimal capital and operating costs. The latter include, in addition to the energy for establishing the necessary operating temperature. the consumption of reducing agents and the energy losses through flow resistance in the catalyst bed (pressure losses). The capital costs are largely determined by the required amounts of catalyst and the associated volumes of the apparatus.

There is additionally the problem of introduction of the reducing agent, which must be mixed .intimately with the gas stream, to be treated, to ensure the best possible efficiency of the reducing agent (avoidance of slip and side reactions) . The mixer required for this should be arranged to be as space-saving as possible, from installation- technical and economic: considerations .

These problems are solved by the apparatus according to the invention.

With the apparatus described below, in particular a method can be carried cut for reducing the content of Μόχ and ih© in gases, in particular in process gases and offgases, which comprises the following measures: a) leading the ϊ%0~ and NQX~containing gas over a succession of two catalyst beds containing one ox more zeolites loaded with iron, b) adding a reducing agent for M3X between the catalyst beds, c) setting a temperature of less than S"0-&»c in the first catalyst bed and the second catalyst bed, d) setting· a gas pressure of at least 2 bar in both catalyst beds, e) selecting a space velocity in the first and second catalyst bed such that a degradation of the h2O content of the gas by at most up to 90%, relative to the N2O content at the inlet of the first catalyst bed, tabes place in the first catalyst bed, and such that further degradation of the %O content of the gas by at least 30%, relative to the N20 content at the inlet of the second catalyst bed, takes place in the second catalyst bed.

Itt the first catalyst bed for pure h30 decomposition, as expected the NOX still present in the gas speeds up the desired hiO decomposition by an activating action, as was described for various 8^5/®* ratios by hdgel ef al. in Canal, Comm. 2 (2 001) .2 73-5. however, notable N2O degradation, can also be achieved in the second catalyst bed by decompositioh to nitrogen and oxygen. This was surprising, as on the one hand the 1TOX content, which activates Ν2θ decomposition, is reduced by adding the reducing agent, and, on the other hand it was expected that the reducing agent added is: adsorbed as an intermediate step on the catalyst surface and thus blocks the active centers for ίί20 deeomposi fc ion. in the operating conditions selected, i.e. increased pressures and in particular a reduced ffi-s/Mh ratio, apparently these effects do sot occur.

The method preferably carried out in the apparatus according to the invention therefore makes it possible to carry oat both the decomposition of n2o, and the reduction of W0z at a lev,· operating temperature and with economical space velocities and at the. same time achieve high rates of degradation of and f?Gs,

The term Space velocity means the quotient of volume fractions of gas mixture (measured at 0ftG and 1.()14 bara) per hour relative to one volume fraction of catalyst. The space velocity can therefore be adjusted by means of the volume flow of the gas and/ or the amount of catalyst.

The gas laden with nitrogen oxides is usually led over the catalyst at a space velocity from 200 to 200 000 hi preferably from 5000: to 1,0Q 000 hl/, in particular from S0.00 to SQ OOO h"A, .relative to the added catalyst volume of the two catalyst beds.

After leaving the first catalyst bed, the content Of hxQ according to the method preferably carried out in the apparatus according to the invention is preferably above 200 ppm, in particular above 3 00 ppm, Tn the first catalyst bed there is at most 30%, preferably at most 80% decrease of the SbQ content present at, the beginning of the first catalyst bed.

After leaving the first catalyst bed, the Nj.0- and ΚΟχ-containing gas is first mixed with a gaseous reducing agent, preferably with Wb, and then led over the cataiyst at. a temperature of preferably Isas than 450"C at the selected space velocity, for slmnltaneous degradation of h2Q (by decomposition) and N0x (by reduction).

In the second catalyst .bed there Is an additional at least 3 0%, preferably at least 40% reduction of the Né) content present at the beginning of the second catalyst bod .

In the apparatus according to the invention, iron-containing zeolites are used in. the first and second catalyst bed. These may be different catalysts in. the respective catalyst beds or preferably the same catalyst.

If there is spatial separation of the catalyst beds, it is possible to adjust the temperature of the second catalyst bed or of the gas stream .entering it by heat abstraction or supply, so that it is lower or higher than in the first catalyst bed.

The temperature of the gas stream in. the first catalyst bed, in ’which only the h20 is degraded, and in the second catalyst bed, in which hjd and NCy are degraded, is, in the: method preferably carried out in the apparatus according to the invention, below 500*0, preferably in the range from 25 G to 500*0, in particular at 30S to 45 0*0, and quite especially preferably at 350 to 4 50*G, The temperature in the second catalyst bed preferably corresponds to the temperature in the first catalyst .bed. The temperature in the catalyst bed can. be determined advantageously as the arithmetic mean of the temperature of the gas stream at catalyst bed inlet and outlet.

The choice of operating temperature is, like the selected space velocities, determined by the desired degree of degradation of :t>0,

Preferably, the temperature, volume flow and amount of catalyst in the first catalyst bed are selected so that there, at most 90%, preferably at most 89% and quite especially preferably at most 70% of the H70 present at the beginning of the first catalyst bed is decomposed-

Preferably, the. temperature, volume flow and amount of catalyst in the second catalyst bed are selected so that further degradation of the h2© content of the gas fey at least '3 0% takes place there, relative to the NSO content at the inlet of the second catalyst bed.

The method preferably carried out in the apparatus according to the invention is carried out at an increased pressure of at least 2 bar, preferably at least 3 bar, quite especially preferably from 4 to 25 bare Feed of the reducing agent between the first end the second catalyst bed, i.e. after; the first and before the second catalyst bed, takes place via a, suitable device, e.g. a suitable pressure valve ox suitably arranged nozzles,

In the first reaction zone, generally a relatively low water concentration is preferred, as a very high water content would necessitate high operating temperatures (e.g. .>5Θ:0°Ο . This could, depending on the type of zeolite used and the operating time,. exceed the hydrothermal stability limits of the catalyst. However, the hOx content has a decisive role .here, as this can offset the deactivation by water.

For the reduction in the second reaction :zone, a high warat content has a minor role, because here. high hey degradation rates are achieved even at relatively low temperatures.

The reducing agent is added in an amount such as is required for reduction of the ΚΟ·,;, This means, in the context of this: description, the amount of reducing agent that is required in order to reduce the proportion, of NOX in the gas mixture completely or to the desired final concentration,, without any notable reduction of the N2o taking place.

Substances that have: high activity and selectivity for reduction of UG2i and whose selectivity 'and activity in the selected reaction conditions is greater' than for possible reduction of h2C>, can be used as reducing agent in the sense of the invention.

For example hydrocarbons, hydrogen, carbon monoxide, ammonia or mixtures thereof, e.g. Synthesis gas, can be used as reducing agent in the sense of the invent.!©», Ammonia or substances that release ammonia when introduced, such as urea or ammonium carbamate, are especially preforrad,

The awotm.fe of reducing agent added should net be notably greater than is necessary for reduction of Κ0χ in the selected reaction conditions.

In the case of ammonia as reducing agent, depending on the desired degree of degradation of the bly content, up to max. 1,2, preferably 1.0 to 1.2 mols fractions of ammonia are used, relative to one mole fraction of hOK. If a lower degree of degradation of NCy is desired, then the amount of mole fractions of ammonia is max, 1., 2*γ, relative to one mole fraction of NCy? where y Is the percentage of the hox that should, be consumed in the reduction.

With, selection of suitable catalysts and process conditions, the SHj added does not act as a reducing agent for tto, but selectively reduces the hQx contained in the: offgas.

The method preferably carried out in the apparatus according to the invention therefore makes it possible to carry out removal of Syo and dtp at a low operating temperature with low consumption of gaseous reducing agent... such as NH3, which was not previously possible with the methods described in the prior art.

This is very advantageous especially when large amounts of H2Q must be removed.

The manner of introducing the gaseous reducing agent into the gas stream to he treated can also be freely arranged in the sense of the invention, provided this takes place in the direction of flow before the second catalyst bed. It can for example take place in the feed line before the vessel for the second catalyst bed or directly before the catalyst bed. 'The reducing agent can be Introduced in the form of a gas or also a liquid or an aqueous solution, which evaporates in the gas stream to be treated.

Catalysts used according to the invention essentially contain., preferably > SO wt-%, in particular > 70 wt.% of one or more zeolites loaded with iron. Thus, for example, in addition to ah Fe-ZSM-S zeolite, another iron-containing zeolite:, e.g. an iron-containing zeolite of the HEX or FBK type, can be contained in the catalyst used according to the invention,

Furthermore, the catalyst used according to the invention can contain other additives known by a person skilled in the art, e.. g. binders.

Catalysts used according to the invention are preferably based on zeolites, into which, iron has: been ineorporated by solid ion exchange. Usually this is based on the commeyciaXly available ammonium zeolites (e.g, Mh~2SM-5) and the corresponding iron salts {e.g. teSOi x 7 H-;0) and these are mixed together thoroughly by mechanical- means in a bail mill at room temperature (Turefc et al. ; Appl, Cabal, ISA, {1399) 249-256; SP-A-6 355 080). Reference is hereby made expressly bo these literature sources, The catalyst powders obtained are then calcined in a chamber furnace in air at temperabures in the range from 4GQ to 600oC. After calcining, the iron-containing zeolites: are washed thoroughly in distilled water and dried after filtering off the zeolite, Finally, suitable binders are added to the iron-containing zeolites obtained and they are mixed and for example. extruded to form cylindrical catalyst bodies, All binders usually employed are suitable as binders, the commonest being aluminium silicates, e.g. kaolin.

According to the present invention, the: zeolites that can be used are loaded with iron. The iron content, relative to the mass of zeolite, can be up to 25%, but is preferably 0.1 to 10%.

Preferably they are zeolites loaded with iron of tape MP I, BSA, PER, MOE, PAU and/or MSI,, in. particular of type 2. AM-.5 .

In. a preferred embodiment, zeolites loaded with iron whose crystal structure has no pores or channels: with crystallographic diameters greater than or equal to 7. G Angstrom, are used at least in the second catalyst bed.

These include zeolites loaded with, iron of type MFl, PER and/or MEL, in particular of type 2SM-5.

The method tarried, put in the apparatus according to the. invention includes eke use of zeolites in which the lattice aluminium is partially substituted isoraorphiealiy by one or more elements., for example is replaced with one or more elements selected from B, Be, Ga, Fe, Cr, V, As, Sb and Bi. Xt also includes the use of zeolites in which the lattice silicon is substituted isomorphically by one or more elements, for example is replaced by one or more elements selected from Ge, Ti, Zr and H£ ,

Precise information on the construction or structure of the zeolites used according to the invention is given, in the Atlas of Zoolite. Structure Types, Elsevier, 4th revised edition 19.96, to which reference is expressly made hereby.

Quite especially preferably, the zeolite catalysts defined above that have been treated with steam {“steamed” catalysts) are used in the method carried out in the apparatus according to the invention. with this treatment, the lattice of the zeolite is dealuminized; this treatment is known per se by a person skilled In the art. Surprisingly, these hydrothermally treated zeolite catalysts are characterized by especially high activity in the method according to the invention,

It is preferable to use hydrothermally treated zeolite: catalysts that have been loaded with, iron and in which the ratio of extralattiee aluminium to lattice aluminium Is at least 1:2, preferably 1:2 to 20:1.

The water content of the reaction gas is preferably .in the range from <25 vol.%, in particular in the range «15 vol.%, A low water content is in general to be preferred.

Generally a relatively low water concentration is preferred, as higher water contents would necessitate higher operating temperatures, Depending on the type of zeolite used and the operating time., this could exceed the hydrothermal stability limits of the catalyst and therefore has to be adjusted to the particular individual case selected.

The presence of C02; and of other deactivating constituents of the reaction gas, which are known by a person skilled in the art, should also be minimized as far as possible, as these would affect the 1770 degradation adversely.

The method preferably carried oat in the apparatus according to the invent ion also works in the presence of o2j as the catalysts used according to the invention have corresponding seiectivities, which at feemperatuxes <500°C suppress reaction of the gaseous reducing agent, such as NH;, wi th 02,

All these influencing factors, and the selected catalyst loading, i.e. space velocity, have to be taken into account when selecting the suitable operating temperature of the reaction zone.

The apparatus according to the invention can be used in particular in nitric acid manufacture, for power station offgases or with gas turbines. In these processes, nitrogen, oxide-containing process gases and offgases are formed, from which nitrogen oxides can be removed economically by means of the apparatus presented here. The apparatus according to the invention is used advantageously for the residual gas from nitric acid production after the absorption tower.

The design of the catalyst beds is optional in the sense of the invention. For example, the catalyst, or the catalysts can he arranged in. a catalyst bed with axial or preferably radial flow, which are housed in one or snore vessels.

The invention relates to an apparatus for reducing the content of H0v and N20 in gases, in particular in process gases and offgases, comprising; A) two series-connected catalyst beds containing one or more zeolites loaded with iron, through which the ©»- and fkO-containing gas passes, and both of which are arranged in a vessel, B} a device arranged between the catalyst, beds for introducing a gaseous reducing agent into the stream of the 'N0x- and. syi-containing gas, comprising a mixer which is a static mixer having appropiate internals or a dynamic mixer and through Which the gas is led after flowing through the first catalyst bed, and comprising a feed line for reducing agent, which opens into the space after the first catalyst bed and before or in the mixer, wherein the gas to be purified, after leaving the mixer, is led through the second catalyst bed and wherein C) at least one of the catalyst beds is arranged in the; form of a hollow cylinder, through which the H0x- and N20~containing gas flows radially.

In the apparatus according to the invention, born catalyst beds are arranged in one vessel, which lowers the equipment co s t s c ons i de r ah 1 y.

According to the. invention, the gas to be purified flows radially through. afc least oh© catalyst bed. preferably both catalyst beds, which results in a greatly reduced pressure loss.

The at least one radial-flaw catalyst bed is arranged in the iora ef a hollow cylinder. Radial-flow catalyst beds can fcx arranged above one another or a combination cf axial- and radial-flow catalyst beds can be selected. In this case, suitably arranged separation plates between the catalyst beds can predetermine the path of the gas, so that it flows first through the first and then rhrough the second catalyst bed.

In the ease of radial-flow catalyst beds,, these can also be in the form cf concentrically arranged hollow cylinders. Again in this embodiment , suitably arranged separation plates are required between the catalyst beds fox predetermining the path of the gas, so that it flows first through the first and then through the second catalyst bed.

In the radial basket reactor, the direction of flow of the gas can he from inside to outside or from outside to inside.

In a preferred embodiment, there are two radial-flow catalyst beds, for example in the form, of two hollow cylinders, with different diffiensioas, wherein the external dimension of the one catalyst bed is smaller than the internal dimension of the other catalyst bed and both catalyst beds are arranged concentrically relative to one another, and wherein suitably arranged separation plates between the catalyst beds predetermine the path of the gas:, so that it flows first through the first and then through the second catalyst bee.

In the apparatus according to the invention, after flowing through the first catalyst bed, the gas is led into a mixer, which is preferably arranged at the center of the apparatus.

The mixer serves .for intimate distribution of the reducing agent in the gas stream. The mixer is a static mixer with corresponding internal fittings or a dynamic mixer.

Figs. 1 to 6 describe preferred embodiments of the apparatus according to the invention in longitudinal section. rig. 1 shows an apparatus according to the invention with gas inlet fl) and gas outlet ¢2} , The first catalyst bed in the form of a hollow cylinder (4) is arranged in the upper internal space opposite the gas inlet f 1) , and is located on a partition., which divides the space of the apparatus into two halves,: Moreover, the upper lateral, surface of the hollow cylinder (4) is closed by a partition. The. gas to be purified flows through the gas inlet (1) and across the annular' gap of the inlet i7) of the first catalyst bed into the annular gap of the outlet (S) of the first catalyst bed radially through the first catalyst bed. From there it flows into the mixer fS), on the inlet side of which a feed line (3) for the reducing agent opens. Mixer (S) is led through the partition and the gas then flows through the annular gap of the inlet (S) of the second catalyst bed (S') arranged under the first catalyst bed (4) into the annular gap of the outlet (10) of the second catalyst bed fs) radially through the second catalyst bed. From there, the purified gas leaves the apparatus via the gas outlet (.2) ,

Fig, 2 describes a similar embodiment to that in. Fig, 1, except that the first catalyst bed (4) is arranged below the second catalyst bed (5) and the gas inlet (1) and gas outlet (2) are arranged laterally in the apparatus·. The other reference symbols have the meanings given in the description of Fig. 1 -

Fig. 3 shows another embodiment of the apparatus according to the invention with gas inlet (1) and gas outlet {2} . The first catalyst had (4) and second catalyst .bed (5) are arranged here as two hollow cylinders arranged concentrically in one another. The first catalyst bed (4) is located outside of a. concentric partition (11),. which closes off the. lower lateral surface of the catalyst, bed (4), the annular gaps (7) and (8) and the internal space of the apparatus and the upper lateral surface of the second catalyst .bed (5) , The gas to be purified enters the apparatus through the gas inlet (1), flows through the first catalyst bed from the annular gap inlet (7) radially from outside to inside into the annular gap outlet (8). From there it flows into the mixer (S). on the inlet side of which a feed line (3); for the reducing agent opens. Mixer (6) opens into the internal space of the second catalyst: bed (5) , which is closed at the bottom by a partition. The gas then flows through the annular gap of the inlet (9) of the second catalyst bed (5) into the annular gap of the outlet (10) of the second catalyst bed (5) radially outwards through the second catalyst bed. From there, the purified gas leaves the apparatus via the gas outlet (2) -

Fig. 4 describes a similar embodiment to that in Fig. 3, except that the first -catalyst bad (4) forms the internal, hollow cylinder and the second catalyst bed (S) forms the outer hollow^ cylinder. The other reference sysbols have the meanings given in the description of Fig, 3,

Fig. S describes an embodiment in which an axial- and a radial-flow catalyst bed are provided. The gas flows via the gas inlet (I) axially through the first catalyst bed (4) and into the mixer (S) . In the apparatus there is a partition, which divides the space of the apparatus into two halves, on tha inlet side of the mixer (S) , a feed line (3} opens, for the reducing agent, From mixer (6). the gas flows into the annular gap of the inlet (9) of the second catalyst bed (5) and through this radially into the annular gap of the outlet (10), From there, the purified gas leaves the apparatus via. tha gas outlet (2) .

Fig, € describes a similar embodiment to that in Fig. 5, except that the first catalyst bed {4) has radial flow and the second catalyst bed {5) has axial flow. The other reference symbols have the meanings given In the description of Fig. 3. A method that is preferably used in the apparatus according to the invention is explained by the following example., A zeolite loaded with iron of the type 2SM-5 was used as catalyst, The production of the Fe-ZSM-5 catalyst was carried out by solid ion exchange starting from: a commercially available zeolite in ammonium form (ALST-RBSTA, SM27). Detailed information on preparation can be found in: 14, Rauscher, K, Kesore, R, Moanig, W. Schwinger, A. Tissler, T3 Turekt !,Treparation of highly active Fe-1814-5 catalyst through solid state ion exchange for the catalytic decomposition of N3O” in Appl. Catal. IS4 (1999) 249-256,

The catalyst powders were calcined in air for Sh at S23R, washed and dried overnight at 383R. After addition of suitable binders, extrusion to cylindrical catalyst bodies was carried out,

As the apparatus fox' reducing the: N0-< and $2o content, two series-connected tubular reactors were used, which were filled in each case with an amount of the above catalyst such that, relative to the incoming gas stream, in each case a. space: velocity of 15 090 h"1 was obtained. 17¾ gas is added between the two reaction sones. The operating temperature of the reaction rones was adjusted by heating. The gas streams entering and leaving the reactors were analysed using an F£TR gas analyzer.

With initial concent rat ions of 1*500 ppm Ss0, 3 SO ppm NOX, 3000 ppm HaO and 1.2 vo.1.% O2 in d2 end intermediate addition of 11¾, with a uniform operating temperature Of 42:5°C and an operating pressure of 6.5 bar, the conversion results for K2O, $0* and :rø3 shown in the following table were obtained:

Table

Claims

An apparatus for reducing the content of NOX and N2O in gases, especially in process gases and exhaust gases, comprising: A) two successively coupled catalyst beds containing one or more ferrous zeolites flowing through the gas containing NOX and N2O, and both of which B is an apparatus for introducing a gaseous reducing agent into the stream of gas containing NOX and N2O, comprising a mixer which is a static mixer, with correspondingly incorporated components or a dynamic mixer, through the gas being passed after flowing through the first catalyst bed, and comprising a reducing agent supply line which opens into the space after the first catalyst bed and before or in the mixer, the gas to be purified after leaving the mixer passing through the second catalyst bed and wherein C) at least one of the catalyst beds is formed in the form of a hollow cylinder which is flowed radially by the gas containing NOX and N2O.

Device according to claim 1, characterized in that the two catalyst sizes are flowed radially by the gas containing NOX and N2O.

Device according to claim 1, characterized in that two radially flowing catalyst bearings are arranged over one another or that a combination of superposed axially and radially flowing catalyst bearings is provided, the path of the gas being predetermined at suitably arranged dividing surfaces between the catalyst beds, so that first flow through the first catalyst bed and subsequently the second catalyst bed.

Device according to claim 1, characterized in that two radially flowing catalyst beds of different dimensions are present, the outer target of one catalyst bed being smaller than the inner target of the other catalyst bed and the two catalyst beds being centrally arranged for the gases are predetermined by suitably arranged separating surfaces between the catalyst beds, so that first the first and then the second catalyst bed is flowed through.

Device according to claim 1, characterized in that, after flowing through the first catalyst bed, the gas is fed to a mixer located in the center of the device.

Device according to claim 1, characterized in that the same catalyst is used in the first and second catalyst beds.

Device according to claim 1, characterized in that the ferrous zeolite (s) is of the type MFI, BEA, FER, MOR, FAU and / or MEL.

Device according to claim 7, characterized in that the ferrous zeolite is of the MFI type.

Device according to claim 1, characterized in that the ferrous zeolite is a Fe-ZSM-5.

Device according to claim 1, characterized in that at least one catalyst bed is used an iron-containing zeolite which has been treated with water vapor.

Device according to claim 1, characterized in that, as catalysts in at least one catalyst bed, ferrous zeolite is used, the ratio of extra-grating aluminum to grating-aluminum being at least 0.5.